Merge "Add KM_MIN_MAC_LENGTH tag to HMAC and AES-GCM keys." into mnc-dev

Author: Alex Klyubin

core/java/android/security/keymaster/KeymasterDefs.java

@@ -51,6 +51,7 @@ private KeymasterDefs() {}
     public static final int KM_TAG_DIGEST = KM_ENUM_REP | 5;
     public static final int KM_TAG_PADDING = KM_ENUM_REP | 6;
     public static final int KM_TAG_CALLER_NONCE = KM_BOOL | 7;
+    public static final int KM_TAG_MIN_MAC_LENGTH = KM_UINT | 8;
 
     public static final int KM_TAG_RESCOPING_ADD = KM_ENUM_REP | 101;
     public static final int KM_TAG_RESCOPING_DEL = KM_ENUM_REP | 102;
@@ -194,6 +195,9 @@ private KeymasterDefs() {}
     public static final int KM_ERROR_KEY_RATE_LIMIT_EXCEEDED = -54;
     public static final int KM_ERROR_CALLER_NONCE_PROHIBITED = -55;
     public static final int KM_ERROR_KEY_MAX_OPS_EXCEEDED = -56;
+    public static final int KM_ERROR_INVALID_MAC_LENGTH = -57;
+    public static final int KM_ERROR_MISSING_MIN_MAC_LENGTH = -58;
+    public static final int KM_ERROR_UNSUPPORTED_MIN_MAC_LENGTH = -59;
     public static final int KM_ERROR_UNIMPLEMENTED = -100;
     public static final int KM_ERROR_VERSION_MISMATCH = -101;
     public static final int KM_ERROR_UNKNOWN_ERROR = -1000;
@@ -237,6 +241,8 @@ private KeymasterDefs() {}
         sErrorCodeToString.put(KM_ERROR_INVALID_NONCE, "Invalid IV");
         sErrorCodeToString.put(KM_ERROR_CALLER_NONCE_PROHIBITED,
                 "Caller-provided IV not permitted");
+        sErrorCodeToString.put(KM_ERROR_INVALID_MAC_LENGTH,
+                "Invalid MAC or authentication tag length");
         sErrorCodeToString.put(KM_ERROR_UNIMPLEMENTED, "Not implemented");
         sErrorCodeToString.put(KM_ERROR_UNKNOWN_ERROR, "Unknown error");
     }

keystore/java/android/security/keystore/AndroidKeyStoreAuthenticatedAESCipherSpi.java

@@ -51,7 +51,7 @@
 abstract class AndroidKeyStoreAuthenticatedAESCipherSpi extends AndroidKeyStoreCipherSpiBase {
 
     abstract static class GCM extends AndroidKeyStoreAuthenticatedAESCipherSpi {
-        private static final int MIN_SUPPORTED_TAG_LENGTH_BITS = 96;
+        static final int MIN_SUPPORTED_TAG_LENGTH_BITS = 96;
         private static final int MAX_SUPPORTED_TAG_LENGTH_BITS = 128;
         private static final int DEFAULT_TAG_LENGTH_BITS = 128;
         private static final int IV_LENGTH_BYTES = 12;

keystore/java/android/security/keystore/AndroidKeyStoreKeyGeneratorSpi.java

@@ -171,7 +171,7 @@ protected void engineInit(AlgorithmParameterSpec params, SecureRandom random)
                         "Key size must be positive: " + mKeySizeBits);
             } else if ((mKeySizeBits % 8) != 0) {
                 throw new InvalidAlgorithmParameterException(
-                        "Key size in must be a multiple of 8: " + mKeySizeBits);
+                        "Key size must be a multiple of 8: " + mKeySizeBits);
             }
 
             try {
@@ -272,6 +272,11 @@ protected SecretKey engineGenerateKey() {
         KeymasterUtils.addUserAuthArgs(args,
                 spec.isUserAuthenticationRequired(),
                 spec.getUserAuthenticationValidityDurationSeconds());
+        KeymasterUtils.addMinMacLengthAuthorizationIfNecessary(
+                args,
+                mKeymasterAlgorithm,
+                mKeymasterBlockModes,
+                mKeymasterDigests);
         args.addDateIfNotNull(KeymasterDefs.KM_TAG_ACTIVE_DATETIME, spec.getKeyValidityStart());
         args.addDateIfNotNull(KeymasterDefs.KM_TAG_ORIGINATION_EXPIRE_DATETIME,
                 spec.getKeyValidityForOriginationEnd());

keystore/java/android/security/keystore/AndroidKeyStoreSpi.java

@@ -672,6 +672,11 @@ private void setSecretKeyEntry(String entryAlias, SecretKey key,
             KeymasterUtils.addUserAuthArgs(args,
                     params.isUserAuthenticationRequired(),
                     params.getUserAuthenticationValidityDurationSeconds());
+            KeymasterUtils.addMinMacLengthAuthorizationIfNecessary(
+                    args,
+                    keymasterAlgorithm,
+                    keymasterBlockModes,
+                    keymasterDigests);
             args.addDateIfNotNull(KeymasterDefs.KM_TAG_ACTIVE_DATETIME,
                     params.getKeyValidityStart());
             args.addDateIfNotNull(KeymasterDefs.KM_TAG_ORIGINATION_EXPIRE_DATETIME,

keystore/java/android/security/keystore/KeymasterUtils.java

@@ -22,6 +22,8 @@
 import android.security.keymaster.KeymasterArguments;
 import android.security.keymaster.KeymasterDefs;
 
+import java.security.ProviderException;
+
 /**
  * @hide
  */
@@ -133,4 +135,45 @@ public static void addUserAuthArgs(KeymasterArguments args,
                     userAuthenticationValidityDurationSeconds);
         }
     }
+
+    /**
+     * Adds {@code KM_TAG_MIN_MAC_LENGTH} tag, if necessary, to the keymaster arguments for
+     * generating or importing a key. This tag may only be needed for symmetric keys (e.g., HMAC,
+     * AES-GCM).
+     */
+    public static void addMinMacLengthAuthorizationIfNecessary(KeymasterArguments args,
+            int keymasterAlgorithm,
+            int[] keymasterBlockModes,
+            int[] keymasterDigests) {
+        switch (keymasterAlgorithm) {
+            case KeymasterDefs.KM_ALGORITHM_AES:
+                if (com.android.internal.util.ArrayUtils.contains(
+                        keymasterBlockModes, KeymasterDefs.KM_MODE_GCM)) {
+                    // AES GCM key needs the minimum length of AEAD tag specified.
+                    args.addUnsignedInt(KeymasterDefs.KM_TAG_MIN_MAC_LENGTH,
+                            AndroidKeyStoreAuthenticatedAESCipherSpi.GCM
+                                    .MIN_SUPPORTED_TAG_LENGTH_BITS);
+                }
+                break;
+            case KeymasterDefs.KM_ALGORITHM_HMAC:
+                // HMAC key needs the minimum length of MAC set to the output size of the associated
+                // digest. This is because we do not offer a way to generate shorter MACs and
+                // don't offer a way to verify MACs (other than by generating them).
+                if (keymasterDigests.length != 1) {
+                    throw new ProviderException(
+                            "Unsupported number of authorized digests for HMAC key: "
+                                    + keymasterDigests.length
+                                    + ". Exactly one digest must be authorized");
+                }
+                int keymasterDigest = keymasterDigests[0];
+                int digestOutputSizeBits = getDigestOutputSizeBits(keymasterDigest);
+                if (digestOutputSizeBits == -1) {
+                    throw new ProviderException(
+                            "HMAC key authorized for unsupported digest: "
+                                    + KeyProperties.Digest.fromKeymaster(keymasterDigest));
+                }
+                args.addUnsignedInt(KeymasterDefs.KM_TAG_MIN_MAC_LENGTH, digestOutputSizeBits);
+                break;
+        }
+    }
 }